Needle shim modification

[Road_Clam]

Too funny I just read this tip, and one of my first mods to any bike that has a slight lean stumble off idle and into the mid range is to shim the needle. Modern bikes come so EPA lean with respect to low speed jetting they run like absolute garbage in cooler temps (like we have up here in New England). I drove our new GZ for about 1/2 hr in colder temps and knew right away my carb need some richening. I have a bunch of 3mm X .020" washers I got from Radio Shack, and they work perfect for shimming needles. I also pulled the "epa" plug for the air fuel screw, and added 1/2 turn CCW for some much needed cold starting ease. Now even if it's 40F, our GZ fires right up on 1/2 choke as soon as I hear elevated clean rpm's I shut the choke off and the engine purrs perfect. No mid range stumble either. I've shimmed needles and many times also have to bump the pilot jet(s) one size richer too, but so far doesn't seem like the GZ will need a richer pilot jet. Great tech thread !

[Road_Clam]

Originally Posted by emory70

how can freeing up the intake and exhaust not make the engine more efficient? .

Easy. The cylinder head port design is most likely the "bottle neck". A combustion engine is simply an air pump. In theory the more air you let in, the more air you need to let out. So one would think that adding a free flowing exhaust, a K&N filter and re-jetting the carb would yield flow and hp gains. BUT if the valves and the intake and or exhaust port design are already at max flow, all your other intake and exhaust flow performance mods are useless. I would bet my left *** that if a GZ owner sent their head out to be velocity ported, AND added a exhaust, filter and re-jet, now I would bet you would feel a substantial difference. But again, the GZ was not engineered to be a stop light to stop light beast... LOL

[blaine]

Originally Posted by Road_Clam

Too funny I just read this tip, and one of my first mods to any bike that has a slight lean stumble off idle and into the mid range is to shim the needle. Modern bikes come so EPA lean with respect to low speed jetting they run like absolute garbage in cooler temps (like we have up here in New England). I drove our new GZ for about 1/2 hr in colder temps and knew right away my carb need some richening. I have a bunch of 3mm X .020" washers I got from Radio Shack, and they work perfect for shimming needles. I also pulled the "epa" plug for the air fuel screw, and added 1/2 turn CCW for some much needed cold starting ease. Now even if it's 40F, our GZ fires right up on 1/2 choke as soon as I hear elevated clean rpm's I shut the choke off and the engine purrs perfect. No mid range stumble either. I've shimmed needles and many times also have to bump the pilot jet(s) one size richer too, but so far doesn't seem like the GZ will need a richer pilot jet. Great tech thread !

Exactly the same with mine.Couldn't believe the difference in cold starting.You wouldn't think it was the same bike.Oh.Welcome to the family.
:cool:

[golem]

I did the needle shimming yesterday and today, while riding, my bike stopped for no reason, it just started to make less noise then stopped all together. I was able to start it again after a couple of tries and get back to work. Do you think it might be related?

[jonathan180iq]

While doing the shim, you mess with a couple of things that could cause an air leak. A big enough air leak and you loose vacuum to draw fuel, which would eventually kill the bike.

Make sure your vacuum hoses are connected.
Make sure your carb boot is secure
Make sure you didn't kink the fuel line
Make sure you didn't pinch the rubber diaphragm under the black plastic cover on top. (That happens a lot)

[golem]

Ok thank you !